Genetic diversity ofFrankiastrains in root nodules fromHippophae¨ rhamnoidesL.

Abstract

The Hippophae¨ rhamnoides L. – Frankia symbiosis is of ecological and practical importance, but very little is known about H. rhamnoides-infective Frankia strains. To address this problem, we have used PCR-restriction fragment length polymorphism (PCR-RFLP) analysis of nifD–nifK intergenic spacer (IGS) to estimate their genetic diversity at 19 sites in Northern China. Restriction analysis indicated that H. rhamnoides-infective Frankia had a high genetic diversity; the samples were divided into nine RFLP patterns (A–I). Elevation and precipitation likely affect the distribution of different Frankia patterns in root nodules. The patterns A and D were present in relatively large areas, which were located at various elevations; however, the distribution of patterns B, C, E, F, G, H, and I generally followed a geographic range. The richness of Frankia diversity was influenced by plant cover and geographic factors such as elevation and precipitation. H. rhamnoides cover had a higher diversity than that of natural vegetation cover. The center part of the geographical range, with intermediate elevation and precipitation, had a higher level of Frankia diversity than that of the west part and east part with high or low elevations and precipitations, respectively. The nifD–nifK IGS regions were sequenced from 28 nodule samples. Phylogenetic analysis showed that H. rhamnoides-infective Frankia strains were all clustered with the Elaeagnus group, and the diversity of this group was quite extensive. Phylogenetic relationships between Hippophae¨ and Elaeagnus-infective Frankia strains were relatively close to each other. Although not very close to either Hippophae¨- or Elaeagnus-infective Frankia strains, Shepherdia -infective strain SCN10a was closer to Hippophae¨-infective strains than to Elaeagnus- infective strains. This is the first detailed report on the genetic diversity and phylogenetic analysis of H. rhamnoides-infective Frankia.